Microelectronic systems are often subject to voltage fluctuations on the power supply rails that deliver power to the various integrated circuit (IC) components that make up the systems. Spikes, oscillations, or other such power supply noise may cause unpredictable circuit responses, or otherwise degrade system performance and reliability. Power supply fluctuations become increasingly problematic as the nominal supply voltage of microelectronic circuits decreases, as with circuits using nanometer technologies designed to operate at lower supply voltages relative to older technologies. For example, some circuits using nanometer technologies are designed to operate at a 0.9 VDC supply voltage, compared with 5 VDC for older systems. As the nominal supply voltage decreases, so does system tolerance to power supply noise.
High frequency digital systems are particularly prone to power supply noise, since sudden changes in the system activity rate may cause spikes, droops, or even temporary oscillations on the voltage supply rails. Power rail spikes and oscillations are also a function of IR drops, or DC voltage drops due to parasitic resistances between the power supply and circuit components. Another source of power supply fluctuations is di/dt noise, or instantaneous voltage variations due to inductive effects on the power lines.
Monitoring the internal supply rail of a microelectronic circuit can be difficult. Although some systems include a monitoring system dedicated to monitoring the internal power supply line, such systems often have limited bandwidth, and consequently can only provide information on relatively low frequency variations on the power supply rails. These monitor systems can be used to compensate for IR and DC drops on the internal supply rails but are inadequate for high frequency noise caused mostly by di/dt fluctuations.
The above-described description is merely intended to provide a contextual overview of current techniques and is not intended to be exhaustive.